The invention relates to an electrosurgical instrument for the coagulation of biological tissues.
Plasma surgery is a method of monopolar high-frequency surgery (HF surgery) in which a high-frequency electrical current (HF current) produced by a high-frequency generator (HF generator) is sent through an ionized noble gas (plasma), for example argon (argon plasma), from an electrical pole within a suitable surgical instrument onto the tissue to be treated and from there is conducted back to the HF generator through a so-called neutral electrode applied to the patient (G. Farin et al.: Technology of Argon Plasma Coagulation with Particular Regard to Endoscopic Applications; Endoscopic Surgery and Allied Technologies, No. 1, Vol. 2, February 1994, 71-77). As a result heat is introduced to the tissue, both endogenously by the HF current and exogenously by the higher temperature of the plasma relative to the tissue, so that the temperature of the tissue rises. Depending on the temperature various thermal effects are caused in the tissue, which can be used by surgeons for various therapeutic purposes such as blood coagulation or hemostasis and/or the thermal devitalization or destruction of pathological tissues (K. E. Grund et al.: Argon Plasma Coagulation in Flexible Endoscopy, Endoscopic Surgery and Allied Technologies, No. 1, Vol. 2, February 1994, 42-46).
A substantial physical prerequisite for plasma surgery is a noble gas, such as the aforementioned argon or helium, which must be present between the electrical pole formed by an electrode within the instrument and the tissue to be treated. The reason is that noble gases can be ionized with relatively low electrical field strengths in comparison to oxygen and/or nitrogen or air, and they do not react chemically with the tissue. Hence the tissue is not carbonized or even vaporized.
Within the last five years plasma surgery, in particular in the course of flexible endoscopy, has found a broad indication spectrum (K. E. Grund: DMW), so that a variety of demands are made with respect to the application techniques and the instruments, HF generators and gas sources required.
The U.S. Pat. No. 5,207,675 discloses an electrosurgical instrument that is problematic inasmuch as the electrode of the instrument can unintentionally come into direct contact with the tissue. Because of the relatively high HF voltage at the electrode, there is thus a risk that in particular thin-walled organs, such as those that are ordinarily present in the gastrointestinal tract and in the tracheobronchial system, may be perforated.
The patent DE 41 39 029 A1 discloses an electrosurgical instrument in which the electrode is disposed within the instrument in such a way that it does not touch the tissue, as long as the instrument is used according to instructions. A problem with this instrument is that the noble gas flows out of one or several openings at the distal end of the instrument in a predetermined direction. As a result the HF current can also flow to the tissue only in this directed (ionized) gas stream. When large-area lesions are to be treated this is disadvantageous inasmuch as the instrument must be moved several times over the tissue to be treated in order that the HF current and thus also the intended thermal effects are applied as uniformly as possible over the entire large area of the lesion.
In DE 195 35 811 C1 an electrosurgical instrument of the kind cited above is disclosed in which a diffusor is provided at the gas outlet, which is intended to prevent a mechanical action on liquid and tissue. In particular during the treatment of large-area lesions, however, it has been found that as a result of the unavoidable or even desired turbulences in the current of noble gas, mixing of the noble gas with the ambient gas (which as a rule is air) occurs, so that the specific advantages of plasma surgery are partially abolished.